1. Field of the Invention
The present invention relates to a focus detection device suitable for a camera.
2. Description of the Related Art
Conventional AF single-lens reflex (SLR) cameras are provided with a focus detection device including a phase-difference AF sensor (CCD focus detection device). The AF sensor includes CCD line sensors and monitor sensors. The CCD line sensors receive object light, integrate (accumulate) the object light, and output the integrated electrical charges as a video signal in pixel units. Each monitor sensor outputs a monitor signal corresponding to the amount of the electrical charges integrated by the associated CCD line sensor. The monitor signal output from each monitor sensor is amplified by an auto gain control (AGC) circuit, and the integration operation for all the CCD line sensors is terminated immediately after it is detected that the monitor signal of any of the monitor sensors reaches a predetermined threshold value. A conventional AF single-lens reflex camera having such a CCD focus detection device is disclosed in Japanese unexamined patent publication Hei09-311270.
However, according to such a conventional CCD focus detection device, when the focus detection device operates in flickering lighting such as fluorescent lighting, the output of the AF sensor fluctuates due the flickering lighting, thus deteriorating the accuracy of focus detection.